Mayor of Chicago, Harrison's a champion of the labor unions. By the time fairground construction gets under way, he's sixty-eight and widowed twice. (This book also gives us some weird trivia surrounding Harrison's diet: he drinks a lot of coffee, and eats watermelon with every meal.)
With four mayoral terms under his belt, Harrison runs again for office. Most view him as a friend of the city's lower classes, and he's admired by the Irish and union men. However, most newspapers in Chicago don't support his fifth term. With the fair representing the new Chicago, Harrison represents the old industrial Chicago of slaughterhouses and stockyards. To Burnham and the others, the city requires new leadership. Harrison loses the mayoral election.
Two years later in 1893, the legions of working class men rock the vote and Harrison is elected into office, serving his fifth term.
Even his opponents recognized that Harrison, despite his privileged roots, made an intensely appealing candidate for the city's lesser tier. He was magnetic. (2.13.28)
Basically, Harrison's a city icon.
He's also the target of a crazed Prendergast, who conjures delusions that Harrison will give him a position once he's re-elected. Harrison's never even heard of the dude. Not getting his way, Prendergast shoots Harrison in his home, and the fair's closing ceremony is transformed into a large memorial service.